This invention is for use in mining operations, particularly the mining of coal, by the method known as "long wall mining," where a heavy, cumbersome cutting machine must be moved under the ground from one location to another.
In long wall mining of coal, the coal is removed from a side face or wall of a long underground corridor which usually extends laterally from the mine entry. The coal is cut or sheared in successive passes from top to bottom along one side face or wall of the corridor by a machine known in the art as a "shear". The shear cuts the coal in a plane parallel with the face of the wall as it moves along a track on the floor of the mine parallel with the face of the coal. The track is known as the pan-line, and as the coal is cut, it falls onto a conveyor belt which carries it to an unloading terminal, usually in the mine entry. The pan line comprises a track with parallel rails, the track being in relatively short sections for easy assembly and removal and having interfitting end sections. At least one rail in each section, usually the one which is the closer to the face of the coal, comprises a specially formed rack bar on which the wheels of the shear roll, and which also has along its length sprocket-like teeth which a sprocket-like driver wheel on the shear engages to effect travel of the machine along the pan line, shearing the coal from the surface of the wall as it travels. Typically, the shear has two large cutting disks which are power driven that cut with a kind of slicing action overlapping swaths of coal from the mine face, one swath above the other. At the end of the pan-line the machine reverses and travels in the opposite direction, again cutting the face of the coal as it moves in the reverse direction.
Not all shears are alike. Some may have the rack rail, which is the nearer to the working face, much higher than the opposite second rail, known as the "trapping shoe rail," against which a shoe on the shear, which braces the shear to keep it vertical and resist the thrust of cutting, may travel. Instead of a shoe, a rigid frame structure of the shear, with a wheel or wheels, may be provided. Still other machines, as here shown, may have a rack rail along each side of the pan line.
As mining operations progress, the shear may have to be transported to a location outside the mine and returned or transferred directly within the mine from one place to another. To accomplish any such move, a crew of workmen is required to transfer the heavy shear from the pan-line onto a flatbed dolly to be then moved from one place to another. Loading and unloading the shear are not only laborious and time-consuming operations, often taking a crew a full shift; but they present danger of serious injury to workmen.